> How effective are those top-of-the-mast "porcupine" discharge devices,
> in your experience? Is it worth a trip up the tower, removing big
> Yagis and lowering the mast, to install one? A lot of wasted time if
> this is not a good solution. My snow static on the upper Yagis is 20
> over. Best way to beat me in a contest is to pray for snow.
Hi Jim,
In most of not all cases, the "charge" you are dealing with is
mostly contained in a cloud or cloud cover. (It can be a cloud of
dust also, I suppose.)
You can NOT bleed off that charge without having a path back to
that "cloud".
The problem with this is we generally call this a "leader". It is
usually followed by a big flash and a boom. If you ever listen to the
precipitation static, you will find it reaches a peak just before a big
lightning flash. Then it dies off, and quickly rebuilds.
The little frizzy things actually are intentional corona generators.
They may work (there seem to be conflicting reports), but if they do
it is because they ionize a large area of surrounding air.
They don't reduce the voltage difference between the cloud and
earth, but the can spread the charge out around the antenna. One
way to look at this is they make an invisible "ball" of ionized air
around themselves. I doubt this ball stays in place or is very
effective if there is any wind.
The problem with receiving is we don't want any corona anywhere
near the antenna, because it is the corona that generates noise!
What you would want is a large blunt area to decrease the voltage
gradient around the antenna.
The reason quads are often a bit less noisy in bad weather is
because they almost always have *very well* insulated elements
that slowly leak off any charge (with the exception of the driven
element) and the elements are "boxy". They don't really have much
of a point sticking out in open space. They don't have much
corona. As a matter of fact, the quad was "invented" to solve a
transmitter-induced corona problem at HCJB radio!
A yagi, especially the top yagi, has all those element tips that are
forced to ground potential (forget that silly little insulator on some
antennas, it won't do "squat" especially when wet) sticking out in
the air. They are almost-perfect corona generators.
Adding a more-perfect corona generator near the antenna will
simply make sure you have noise near the antenna.
Anyone who has worked 160 meter mobile can attest to the fact
that the balls on the ends of whips greatly reduce corona! It would
help with a yagi and is actually necessary with some yagis used in
super high power applications, like CB radio.
73, Tom W8JI
w8ji@contesting.com
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